In many countries and locations, it is a common practice to discharge untreated wastewater directly back into the environment. Often, this is due to a lack of funding. However, spatial restrictions, especially for coastal towns where the installation of large treatment facilities is not an option, also play a large role when there is an inability (or lack of willingness) to provide wastewater with proper treatment prior to discharge into the environment.
Even when there exists some form of treatment of wastewater, this treatment is often inadequate and/or inefficient. For example, oxidation ponds, which are in common use in developing countries, normally have an undesirably large retention time of approximately seven to eight days. Moreover, oxidation ponds generally require energy consumptive and inefficient aeration practices, and require prohibitively large areas to be effective. In addition, with oxidation ponds, not only does a significant amount of the present soaps remain in the treatment wastewater, but the discharge from these ponds also generally includes very high levels of suspended solids, bacteria concentrations, and non-polar, insoluble substances such as fats, oils, and greases (FOGs). It will be understood that, as used herein, grease refers to a long-chain hydrocarbon molecule, which is made up of hydrogen and carbon. The terms fats and oils, as used herein, also refer to molecules made up of hydrocarbons.
Flotation technologies also are currently used in a variety of wastewater applications, where coagulants and flocculants are added to the wastewater being treated to assist the flotation of the desired components to be removed. In general, once the components to be removed have risen to the surface of the wastewater being treated, they are skimmed off (removed from) the wastewater and disposed of in an appropriate manner. As is the case with oxidation ponds, however, these flotation technologies have several disadvantages, due to the requirement that coagulants and flocculants be added and for other reasons as well. For example, such flotation technologies often include complex systems that require a high level of maintenance, and often also require high pressures and constant monitoring by experienced individuals.
Ultraviolet (UV) light, which can act as a disinfectant in water due to the fact that radiation in high doses can permanently damage the cellular structure of bacteria and viruses, has also been used to treat wastewater. For example, several treatments include UV lights submerged in a tank containing the wastewater to be treated. In some of these treatments, ozone, which is also commonly used as a disinfectant in water because it is a powerful oxidant, is bubbled up through the bottom of the tank through the wastewater. The effectiveness of methods using UV lights has been limited, however, due to the limited interaction between the wastewater and the UV lights. For example, UV penetration of the wastewater (and interaction with ozone, when it is being used) is often decreased because the exteriors of the UV lights being used are subject to fouling by the contaminants contained in the wastewater. Additionally, for example, wastewaters with high levels of turbidity and suspended solids, and high color values, inhibit UV transmittance, thereby reducing the effectiveness assocaited with the use of UV lights in past treatment systems.
Accordingly, it is desirable to provide methods and systems for the treatment of wastewater that alleviate several of the problems associated with existing treatments. It is also desirable to provide methods and systems for improved treatment of wastewater.